Sciencemadness Discussion Board

ester with bleach

bobpage - 27-10-2008 at 03:24

hi, if anyone could help I would be very appreciative. my class is very hard and I'm trying to study but some of the questions are difficult to answer.

1. (this is easy:) what happens when dodecyl hydrogen sulfate is mixed with NaOH?
this is the normal 'soap' reaction, easy to find on the net, where Sodium attaches to the end of the ester and water is formed.

2. (hard!) what happens when dodecyl hydrogen sulfate is mixed with conc. NaOCl?
well, I think that maybe it is the same as (1). but it would form HOCl instead of water.. so maybe the equilibrium isn't there??

so is it forming some kind of dodecyl hypochlorite instead, as well as NaHSO4? because at least then there is a salt of a strong acid, which is more stable (?)

the thing I don't get is, what governs the reaction? sulfate is a good leaving group, but is it better than HOCl? not even sure if that is the right question. :(

thanks, bobbie

Ebao-lu - 27-10-2008 at 09:10

I think your first suppose was correct (sodium salt + HOCl). But in that case, the question should not be related to "hard" ( is it indeen in that group)?
The alkyl sulphonyl ester salts can also undergo SN2 reaction with nucleophiles(Nu), to form Alk-Nu(in your case dodecyl alcohol) and SO4(2-). But this reaction even with short-chained alkyl hydrogen sulphates is rather slow at r.t., and still in basic solutions it may be possible. So, if dont have excess of NaOH, write 1st answer.
In case of excess of hypochlorite, i think nothing will happen or at least equilibrium OH- will react first, but dont wriite all that about sn2 if nothing else is not specially mentioned there in task

[Edited on 27-10-2008 by Ebao-lu]

bobpage - 28-10-2008 at 04:57

Thanks Ebaolu.. I said sodium salt but was told the answer is wrong, i'm not sure where to go from there. it isnt covered well in the textbook so i tried to find the answer on the net and it is very hard to find. so maybe I will say an alcohol, thanks..

Ebao-lu - 29-10-2008 at 02:46

Yes, this seems to be a hard task now:)
I was surprised to learn, that hypochlorite is a stronger nucleophile then OH-
http://biochemistry.wur.nl/Biochem/educatio/Colleges/Maurice...
And it can react as nucleophilic catalyst in hydrolysis of organic phosphstes and other esters, also used for hydrolysis of phosphororganic military CW agents.. I wonder if this can be extrapolated on sulphates as well, to form alcohols and intermediate slufohypochlorite, that are further hydrolysed to hypochlorite and sulphate. As for Sn2 route, in theory it can also be observed here with OCl-, but there can be many products of further dodecylhypochlorite decomposion - dodecylaldehyde, dodecyl alcohol, dodecene-1-epoxide, noone can guess what is the major. And till she answer should contain only one, i think Sn2 route is not correct suppose.
As for Sn2 path with OH-, i've searched in google and found no mathes of SDS alkaline hydrolysis, so i guess it will not do here

Ebao-lu - 29-10-2008 at 02:48

And was the answer incorrect for 2nd question, or 1st as well?

Ebao-lu - 16-12-2008 at 02:48

So, what was the correct answer?

DJF90 - 17-12-2008 at 10:27

Wouldnt the hydroxide hydrolise the sulphuric acid ester to form dodecanol? I'm not sure if the OH- works like this but water definately does (I think this is the industrial process for ethanol from ethene). Not sure about the hypochlorite though.

Ebao-lu - 17-12-2008 at 16:59

I guess no, because sodium dodecyl sulphate(SDS) is a commanly used SAC, its solutions can be stored easily. But maybe in its acid form (R-O-SO3H), it would have hydrolysed easier, that is probably the case with ethanol from ethene

[Edited on 17-12-2008 by Ebao-lu]

DJF90 - 18-12-2008 at 05:36

Yes that is the case with ethanol from ethene as water is used to hydrolyse the ethyl hydrogensulphate, not NaOH. It was just a desperate stab in the dark as it appears from a previous post that the sodium salt is not the product. I know SDS is stable in aqueous solution, but is this stability present in high pH? If not I would predict that dodecanol, sodium sulphate and water be the products (R-OSO3 + 2NaOH)

Ebao-lu - 19-12-2008 at 00:37

I've tried to find any mathes in google by words "SDS basic(alkaline) hydrolysis" and found nothing, (but found plenty of "acidic" mathes).
Concerning high pH solutions:
Quote:
Five sputum samples and five bronchial aspirates from patients
without tuberculosis were decontaminated by the standard
method of Tacquet and Tisson (15). Briefly, 2 or 3 ml of
the specimens was transferred to a 50-ml plastic centrifuge
tube, and an equal volume of SDS-NaOH solution (2% NaOH,
3% SDS [Fluka Chemical Company, Buchs, Switzerland]) was
added; after being vortexed, the samples were vigorously
shaken for 30 min.

This Fluka solution seems to be sold and stored. 3% NaOH is 0.75M solution and is having pH 12-13.
Maybe in more concentrated solutions SDS is hydrolysed, but that is not mentioned in the task.

[Edited on 19-12-2008 by Ebao-lu]

DJF90 - 19-12-2008 at 06:46

Dont forget we are talking about the free acid, not the sodium salt. If the sodium salt is for some reason not produced by adding NaOH to the dodecyl hydrogen sulphate (as suggested by the original poster) then nucleohilic substitution may be a possibility, leading to dodecanol as I have suggested. However I find it incrediably strange that a simple acid base reaction does not occur (yeilding SDS). I think however that the original poster is mistaken when they say that SDS is not formed.

Ebao-lu - 23-12-2008 at 02:25

I think that Sn2 reaction prior to deprotonation will hardly take place. Actually, i've asked bobpage wether SDS answer was wrong for 1st or 2nd task, but he is probably not reading this topic any more